How to decide between two travel destinations

Compare them on three things: what you want to do there, how much time and money you actually have, and when you can realistically go. Pick the one that solves for all three without compromise.

1. Write down what you want from this trip. Be specific. Not 'relax' but 'swim in warm water and read books on a beach.' Not 'see culture' but 'visit museums, eat local food, walk old neighborhoods.' Spend 5 minutes per destination. This is the only step that matters if you get the rest wrong.
2. Check your actual calendar. Look at your calendar for the next 6 months. How many consecutive days off do you have? When are they? Don't assume you can negotiate time. If one destination needs 2 weeks and you have 10 days, it's already out.
3. Calculate real trip costs. For each destination: flights from your city (check right now on Google Flights), 3 nights accommodation (mid-range, no luxury), food per day (research 5 restaurant prices), local transport. Add 20% buffer. Write the total. Compare to what you can actually spend.
4. Check what time of year works. Look up the best season for each destination and when you're actually available. If your time off is February and one destination is monsoon season, that's a problem. If the other is perfect in February, you have your answer.
5. Run the weather test. Go to Weather Underground and check average temperature, humidity, and rainfall for both destinations during your actual travel dates. If you hate humidity and one is 85% humid in your travel window, cross it off.
6. Ask the one question that breaks ties. If you still can't decide: which one would you regret not going to in 5 years? Your gut knows. Go with that.

What if I love both destinations equally?

You don't. Something tips it—one has better timing, one costs less, one has something the other doesn't. Ask yourself: which one do my friends keep saying I should visit? Which one would feel like a waste if I went and it rained the whole time? That's your answer.

Should I pick the cheaper one?

Not necessarily. A $1,200 trip where you do exactly what you want beats a $800 trip where you compromise the whole time. Pick based on the fit first, then look at cost. If they're similar cost, cheaper wins. If one is much cheaper but you're lukewarm about it, that's the wrong reason to pick it.

What if one destination requires me to take time off I haven't requested yet?

That one is not an option. Not yet. Decide between destinations you can actually reach with the time and flexibility you have right now. Once you pick, then ask for the time off.

Is it worth going somewhere just because it's trendy?

No. Go because you actually want to do something there. If the trendy place is also where you want to go, fine. But 'everyone's going' is not a reason that holds up when you're spending your money and time.

What if I'm still stuck after all this?

Flip a coin. If you're genuinely tied after honest comparison, it means both work. Pick one and go. You can go to the other one next year. The worst decision is not going anywhere because you can't choose.